First year university physics student here, and I need assistance finding the kinetic energy of an object (specifically, a mousetrap car our lab team built).
I already found the speed, acceleration, net force, and work, we were given the Ek of the mousetrap spring (100N/cm = 1J), I already know the equation to find Ek (1/2 mv^2), and I know energy is conserved, not created, not destroyed, etc.
The question is, using the values I have, how do I complete the energy conservation calculations?
I can provide data from the trials if needed.
In before "lol failure", it's only a bullshit degree breadth course I'm required to take.
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Anonymous2010-01-25 0:12
Initial Kinetic energy is equal to final kinetic energy.
1/2mv^2 = 1/2mv^2 prime.
the kinetic energy of the spring will equal whatever energy it took to move the car a certain distance.
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Anonymous2010-01-25 0:21
>>2
i'm a first year physicist myself, but doesn't that require 100% efficiency?
You have to factor in frictional forces for the deceleration, e.g. the frictional force acts opposite to the direction of travel, and thus does work on the car to make it stop. How much energy is dissipated by friction is dependent of the type of surface the car was on and the weight of the car.
>>3
springs have near 100% efficiency unless you spring them so hard they melt or some shit
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Anonymous2010-01-25 13:32
the kinetic energy decreases in time as the car is slowing down...
1/2*k*x^2 = 1/2*m*v(t)^2-int(F*dx,x=0..A)
Assuming the spring delivers 100% of it's energy, the energy of the spring is the total energy the car will revieve, this is equal to the speed at time t minus the frictional force * the distance traversed. Do you want me to do the math on the right hand side??
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Anonymous2010-01-25 20:24
E_{spring}= \frac{1}{2}k\delta x^2 . Set this equal to the kinetic energy after it's released.
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Anonymous2010-01-28 1:51
1/2*k*x^2 = 1/2*m*v(t)^2-int(F*dx,x=0..A)
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Anonymous2010-01-28 5:35
>>7
What the fuck do, x, int, k, dx and 0..A mean? Does t even mean time and F mean force? What's so difficult about using proper symbols instead of being an obscurant douche?
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Anonymous2010-01-28 11:41
>>10
No >>7 but k is spring constant, x is displacement of spring from equilibrium, int is text shorthand from writing an integral. If you don't know how integrals work, explaining the rest would be futile.
Yes t is time (it indicates the velocity is non-uniform, but a function of time), and F is force.
These actually are the proper and commonly understood symbols for these terms and concepts. Nothing obscurist about it.
>>11 >>12
Wow, same person, you are clearly a genius for being at the right place at the right time to memorise those particular letters.
k means any constant, x could represent anything, not everyone has encyclopedic knowledge of text shorthand and "If you don't know how integrals work" just goes to support my assertion that you are an obscurant douche.
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Anonymous2010-01-30 11:41
>>13
Not >>10 (or >>7), but I thought he was rather polite given how rude you were. Like he said, those ARE the proper and commonly understood symbols for these terms and concepts. I haven't taken a physics class in like 6 years (AP physics, in high school), and I [u]still[u] remember these abbreviations. Anyone familiar with Newtonian mechanics (covered in any introductory physics class) could tell you these are the standard abbreviations; they are in no way obscure. Integrals are the mathematical calculation of the area under a curve, and it's perfectly understandable that he didn't want give a short summary of elementary calculus to sate you.